modern pollen rain in finnish lapland investigated by analysis of surface moss samples

Modern Pollen Rain in Finnish Lapland Investigated by Analysis of Surface Moss SamplesAuthor(s): Sheila HicksSource: New Phytologist, Vol. 78, No. 3 (May, 1977), pp. 715-734Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2434540 .

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New Phytol. (1977) 78, 715-734.

MODERN POLLEN RAIN IN FINNISH LAPLAND INVESTIGATED BY ANALYSIS OF SURFACE MOSS SAMPLES

BY SHEILA HICKS

Department of Botany, University of Oulu, Finland

(Received 16 November 1976)

SUMMARY The results of pollen analyses from ten surface moss samples collected from the different regional vegetation types of northern Finland are presented. The main features distinguishing the pollen assemblages and the trends observable in transecting the series of vegetation types are outlined and compared with the results of similar studies from elsewhere. With the aim of using the modem pollen assemblages to interpret fossil ones, a simple graphical method of classifying the boreal assemblages is given and specific limits for the forest types presented are suggested. The inability of this graph to distinguish 'tundra' assemblages is noted and additional criteria for separating out this regional type are detailed. Emphasis is also placed on the importance of having absolute pollen frequency values to supplement the relative ones-

INTRODUCTION

Pollen analysts have become increasingly aware of the fact that a realistic interpretation of the vegetation changes represented in pollen diagrams from lake sediments and peat profiles is greatly facilitated if the relationship between the vegetation surrounding a catchment site and the pollen falling on that site is known (see Birks, 1973, for a detailed presentation of the different approaches to the reconstruction of past vegetation on the basis of pollen assemblages). To this end an ever-growing number of studies have concentrated on establish- ing this relationship either by analysing surface lake sediments and/or moss samples (e.g. Davis, 1967a; Bartley, 1967; Fredskild, 1967; Lichti-Federovich and Ritchie, 1968; Davis, Brubaker and Beiswenger, 1971; Birks, 1973; O'Sullivan, 1973; Rymer, 1973; Tinsley and Smith, 1974) or by using some kind of pollen trap (e.g. Tauber, 1965; Davis, 1967b; Peck, 1973; Berglund, 1973; Fredskild, 1973; Ritchie, 1974; Hicks, 1974). In general, pollen trap results are to be preferred in that the time period over which the pollen is collected can be controlled and so values/cm2/year can be calculated. Not only can such values be compared directly with pollen influx values whenever absolute pollen frequency data is available but in some instances these values are the only means of distinguishing two otherwise similar pollen assemblages. However, due to annual variations, trap results will only be truly reliable if figures are available for a series of consecutive years. Therefore many workers have been pre- pared to forgo the time dimension and consider only relative values by using moss and surface lake sediment samples. In this case, the pollen extracted is taken as representing the past few years (the exact number of years being indeterminable), so that the results are held to be free of wild yearly fluctuations.

Although in North America modem pollen rain studies have dealt with vegetation belts on a continental scale (Davis, 1967a; Lichti-Federovich and Ritchie, 1968) recent Euro- pean studies have tended to look at changes over a smaller area, considering variations at a

715



716 SHEILA HICKS

local level rather than on a wide regional basis (Anderson, 1967; O'Sullivan, 1973; Berglund, 1973; Birks, 1973; Rymer, 1973; Vuorela, 1973; Tinsley and Smith, 1974; Hicks, 1974). One factor in this type of study is the uncertaintly as to the size of the catchment area. Although the major proportion of the pollen reaching a site is of relatively local origin (see Tauber, 1967; Peck, 1973) is has been well demonstrated that pollen can be transported over incredibly long distances (see Aartolahti and Kulmala, 1969; Lundqvist and Bengtsson, 1970). Although these last cases represent an extreme situation they are a salutary reminder of the possible significance of long distance transport pollen. Similarly, if a series of sampling sites, even though representing distinct vegetation communities, are situated relatively close to one another, their catchment areas may overlap to the extent that the results are 'blurred' by interference from adjacent communities (Oldfield, 1970). In effect all the samples will exhibit the same characteristic regional pollen assemblage even though having distinctly different local pollen components (Janssen, 1973).

In most parts of north-west Europe investigations on a regional scale are hindered by the overwhelming human impact on the natural landscape and the resulting absence of wide expanses of undisturbed vegetation. However, in northem Fennoscandia one does still find large areas of boreal forest which, although managed, are not so very different in floral composition from the indigenous forests. This area, where human interference is at a minimum, provides one of the few regions of any size in which pollen rain studies even vaguely on a scale comparable with those of North America can be undertaken.

It was in just this part of Europe, in northern Finland, that the pioneer work in the field of modem pollen rain studies was carried out (Auer, 1927; Firbas, 1934; Aario, 1940) and Aario's results from 1940 are, to this day, some of the most quoted for tundra and boreal forest environments. Unfortunately, with the loss of Finland's access to the Arctic Ocean in 1944 a true tundra vegetation is no longer accessible, but northem Finland still provides a complete range of northem boreal vegetation types. A reinvestigation of the pollen rain Within these using techniques which were not available to Aario now seems in order, and to this end a long-term pollen trapping programme was commenced in the summer of 1974. At the same time as the pollen traps were put in position, surface moss samples were collected from a representative number of the sites to provide a guide to the type of pollen spectra to be expected from the traps. It is these preliminary moss sample analyses which are presented and discussed here.

THE SAMPLING SITES

Ten sites are considered, of which three are hill/mountain top localities and the remainder are the central points of medium/small open mires. Their positioning within the vegetation zones of north-west Europe as defined by Ahti, Hamet-Ahti and Jalas (1968) is shown in Fig. 1, from which it is seen that the sub-oceanic, indifferent and slightly continental sections of the northem boreal zone are all represented, together with one middle boreal site and one from the middle/northern boreal zone boundary. In addition the sites are located with respect to the different forest types and the forest density in the maps in Fig. 2. The information used for constructing these maps comes from the Fifth National Forest Inven- tory (see Salminen, 1973) which considers those trees which are at least 2.5 cm in diameter at breast height, and which provides figures for the individual tree species in terms of the volume of standing timber. Although, for most of the country systematic sampling of tract inventory areas forms the basis of the results, for the extreme north air photographs have



Pollen rain in Lapland 717 24e E 28e E

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ThFpeise naosture of eachlindiida siteswti ise summtarionzoesad inTbet1,n fom whic itop isei dent tabot tother p etgey rpresenanc onti diff eren, treeless v ating( 12 hrough topouetemp nFig. 2. Postro all smpigitswhn tese veetations threonehoest andtuationsoN.Erp as pe senedfine byg Ahtis Hamgenerahtizend Jalsne.8

The precise nature of each individual site is summarized in Table 1, from which it is evident that together they represent a continuum from open, treeless vegetation (J 12) through birch woodland (Kil 11, Ke 8) to pine forest (P 9 (boundary), N 7), with additional exam- ples of pine-spruce (A 5, H 14) and spruce dominated (K 2) forests. It should be pointed out that the J 12 sample, although the nearest to a tundra sample that one can find in Fin- land, is more strictly alpine than arctic (Eurola, 1974).



718 SHEILA HICKS

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METHODS

At each site an area with a continuous moss carpet was selected. Small glass jars with a diameter of 4.5 cm were inverted over the moss, cut round with a sharp knife, and pushed into the moss to a depth of 3-4 cm. Any excess was trimmed across with a knife and a tightly fitting cap screwed on. In this way, approximately equal volumes were obtained and the samples were of constant surface area. Whenever possible Sphagnum was chosen, but on the two highest summits no convenient Sphagnum carpets were available and the mosses chosen, being ones growing on shallow mineral soil, did not fill the jars to the same depth. The species composition of the samples was as follows:

J 12 Dicranum fuscescens Tuzn + A nthelia julacea (L.) Dum. Pal 10 Dicranum fuscescens Tuzn. R 1 Sphagnum nemoreum Scop. Kil 11 S. nemoreum Scop. Ke 8 S. nemoreum Scop. P 9 S. fuscum Klingg. + Mylia anomala (Hook. ) Gray N 7 Sphagnum papillosum Lindb. A 5 S. papillosum Lindb. K 2 S. fuscum Klingg. H 14 S. fuscum Klingg.

In the laboratory the samples were weighed, placed in beakers, covered with 10% KOH and heated gently for 1 h, after which each was passed through a metal sieve, rinsed thoroughly with distilled water several times, and all the liquid, including the various rinsing waters, centrifuged. The resulting centrifugate was acetolysed, washed with distilled water, stained with fuchsin and centrifuged in glycerol. Three slides mounted in glycerol were pre- *pared for each sample.

The preparation followed, with slight modifications, that suggested by Jorgensen (1967) for absolute counting, so that the total amount of pollen contained within each sample could be calculated. Since, for each sample, complete slides were always counted, the total number of pollen grains and spores varies, but SAP was always at least 200 and in half the cases over 500. Similarly, EP (ex. spores) was always more than 300 and in four cases more than 1000. The absolute counts for each sample were reduced to a common denominator of 30 g of fresh moss. This gives grains/unit weight values which are comparable within this sample series, but these figures are not in any way to be confused with the grains/cm2/year values which are obtainable from pollen traps. Since two of the samples were of a completely different moss type and therefore present an additional uncontrollable variable, absolute values were not calculated for the three hill/mountain summit sites.

An attempt was made to distinguish between the pollen of the tree birches and that of Betula nana. Rather than taking a strict size criterion (e.g. Birks, 1968; Berglund and Diger- feldt, 1970) or the change in the average size of grains between samples (e.g. Fredskild, 1973; Reynaud, 1974) a combination of size and morphological factors (see e.g. Terasmae, 1951) was used such that all grains with a spherical cross section, relatively delicated exine and low pore which were generally of small size were counted as B. nana, while larger grains with a triangular cross section, robust exine and obviously protruding pore were counted as tree birch. Doubtful cases were included as tree birch, so that the B. nana curve can be considered as a minimum one.



720 SHEILA HICKS

Table 1. Location and description of sampling sites

Site Position Description of Alti- Percentage of Zone and section location tude land covered (Ahti, Hamet-Ahti

(m) by forest and Jalas, 1968) (Salminen,

1973) J 12 69005'N 20'50'E Summit of Jeahkkas' 960 0-10 N. Boreal, suboceanic Pal 10 68003'N 240 1'OE Summit of Palkaskero 710 50-60 N. Boreal, slightly

continental R 1 66014'N 28034'E Northernmost summit 450 60-70 N. Boreal, slightly

of Riisitunturi oceanic

Kil 11 69001'N 20051'E Kilpisjrvi, 0.75 km 480 0-10 N. Boreal, suboceanic S. of the hotel

Ke 8 69045'N 27005'E Kevo, 1.5 km S.W. of 190 0-10 N. Boreal, indifferent field station

P 9 69016'N 27012'E Palomaa, just W. of 210 20-30 N. Boreal, indifferent/ the Inari-Utsjoki road slightly continental 89.5 km N. of Inari

N 7 68052'N 28022'E Nellimo, E. of the 130 80-90 N. Boreal, indifferent Ivalo-Nellimo road 2.5 km N.E. of Nellimo

A 5 66035'N 25051E Apukka, 2 km W.N.W. 105 60-70 N./M. Boreal of the Agricultural Research Station

K 2 66007'N 29000'E Kangerjoki, 20 km 288 60-70 N. Boreal, slightly N.N.W. of Kuusamo oceanic village

H 14 64055'N 25038'E Haukkasuo, 6 km 30 40-50 M. Boreal E.S.E. of Kempele village

RESULTS

The results are presented in the form of a conventional relative pollen diagram in Fig. 3, where the hill summit sites are shown at the top in order of increasing northerliness and altitude, and the mire sites below them similarly arranged from south to north. Although Kil 11 is geographically south of Ke 8 and P 9, because of its greater altitude it is more northerly in vegetational terms and so is placed above Ke 8. The northern limit of pine forest is also indicated.

Local arboreal taxa (AP) (Betula, Pinus, Picea, Alnus), 'exotic' arboreal taxa (in this case only Quercus is represented) and shrubs are shown as % AP, while non-arboreal taxa (NAP) are shown as % NAP. The spores, of which Sphagnum is understandably the most abundant, are not illustrated, but their values as % NAP are set out in Table 2 together with the values of those pollen types included in the curves 'cultural indicators' and 'varia'. Fig. 3 also illus- trates total trees, shrubs and herbs as 2P (ex. spores), and the pollen concentration values for the mire sites as grains/unit weight (AP and total P (ex spores)). To the right of the NAP section of the diagram is a table indicating the composition of the forest in the vicinity of each site, in terms of the dominant tree species, commonly occurring species (Present 1) and occasional species or species present in quantity but at a greater distance (Present 2).

The similarity to Aario's results is immediately noticeable. If the sites J 12, Kil 11, Ke 8, P 9, N 7, and A 5 are compared with Aarios's sites I-VII then the Pinus, Betula and Picea curves together with the AP concentration curve are seen to exhibit the same patterns




Regional forest type Local vegetation (Salminen, 1973)

Birch woodland Alpine dwarf-shrub heath with Dryas octopetala and Cassiope tetragona 40-50% pine, 30-40% Alpine dwarf-shrub heath with Empetrum hermaphroditum and Phyllodoce spruce, 10-20% birch caerula, but including areas of boulder field 40-50% pine, 40-50% Empetrum-Calluna-Eriophorum heath with small scattered Picea and a few spruce, 10-20% birch Pinus

Birch woodland Low-growing Betula dominated forest with some Salix and Juniperus.

Birch woodland Betula forest with a few large isolated Pinus.

80-90% pine, 0-10% Betula forest with a small admixture of Pinus. At the boundary of continuous spruce, 10-20% birch pine forest

80-90% pine, 0-10% Pinus dominated forest with a few Betula spruce, 10-20% birch

30-40% pine, 20-30% Primarily Pinus forest but with areas of Picea and some felled areas spruce, 20-30% birch

30-40% pine, 60-70% Mixed forest of Pinus, Betula and Picea with some Salix. spruce, 10-20% birch

60-70% pine, 10-20% Predominantly Pinus forest but with Betula, Alnus and Populus present spruce, 10-20% birch

although at slightly different values. The high pine-low birch assemblage characteristic of Aario's tundra site I is missing, as would be expected since true tundra vegetation was not sampled. The overall compatability is exactly as expected. The main feature in which the present results differ from those of Aario is in the NAP component. However, since this must be largely of local origin (see below) a discrepancy in this aspect is not surprising.

The main features can be summarized as follows.

Mire sites (1) In moving from south to north across the northern boundary of pine forest (N 7-

P 9-Ke 8-Kil 11) Pinus percentages fall and Betula percentages rise, and both the arboreal and total pollen concentration values fall. The changes from high pine to high birch reflects the change from pine-dominated to birch-dominated forest (Fig. 2a), while the falling arboreal pollen concentration values are taken as resulting from a thinning out of the forest (Fig. 2b). The possibility that this fall may be due to the differential pollen production of pine and birch must not be ignored, but since, in S. Finland at any rate, R values for Betula and Pinus are 2.5 and 0.84 respectively (Donner, 1972), this seems a less likely reason.

(2) Only in the three most southerly sites H 14, K 2 and A 5, where spruce is present in the vegetation, are Picea values at all significant (although even here they are less than 20% AP) and of those the highest spruce values are recorded at the only spruce-dominated site, K 2. Arboreal pollen concentration is variable, reaching almost as high as the N 7 values at A 5 but being particularly low at K 2. These features are both interpreted as reflecting the generally low pollen production of spruce (Donner, 1972; Hicks, 1974, 1975). If the dominant tree in a well-forested region is a low pollen producer then the total AP concentration



722 SHEILA HICKS

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724 SHEILA HICKS

will automatically be very low and at the same time the relative values for the pollen of non- dominant but high pollen-producing species will be artificially high. The situation is less extreme at A 5 and H 14, at both of which sites there is a much greater proportion of pine in the forest.

(3) At most sites Alnus values are very low, the highest percentages being recorded at the most southerly site, H 14 (5.5% AP). This site is also nearest the coast, where alder is a common component of the vegetation (Siira, 1970), and the pollen values obviously reflect this.

(4) At all sites NAP (herb) percentages are less than 35% XP but the variation from site to site is considerable with the lowest values (5.5%O) being recorded as N 7. From the species composition it is evident that a large part of the herb pollen is being produced by plants probably growing on the mire (e.g. Cyperaceae, Ericales, Rubus chamaemorus). The NAP, therefore, represents, in part, fairly local vegetation.

NAP percentages increase from N 7 northwards as AP percentages decrease. Since total pollen concentration is also decreasing the real increase in herb pollen is not as great as the percentage figures would suggest. It is nevertheless real (NAP concentration N 7 -5,327, P 9 -8,924, Ke 8 -9,542, Kil 11 -12,803) reflecting the increasing openness of the forest and the consequent greater abundance of herbaceous plants. The NAP concentration values at the more southern sites are somewhat higher (H 14 -37,326, K 2 -13,623, A 5 -22,065) per- haps reflecting the greater amount of open cultivated land near these sites. The presence of cultural indicators including Urtica and Rumex acetosa type preferentially at these sites would confirm this.

Hill summit sites (1) For all three hill summit sites Pnus values are over 40% AP even though pine is not

an important component of the vegetation. This pine pollen is considered to be long-distance transported. The distance involved,however, need not be as great as the maps in Fig. 2 would suggest since although both Ke 8 and Kil 11 are north of the northern limit of pine forest, isolated pines are found relatively locally and pine forest occurs again along the north Nor- wegian coast (see Hustich, 1958; Federley, 1972).

(2) All sites have birch values between 25% and 50% AP, with the highest values being recorded at the one site (J 12) where the surrounding forest is purely birch. Similarly the highest spruce values are recorded at the one site (R 1) where the regional forest type is spruce, although as in the case of the mire sites the actual percentage of spruce is relatively low.

(3) Of the three sites, J 12 rises well above the tree limit, Pal 10 is noticeably treeless and R 1 only just rises above the forest, still supporting individual stunted trees on its summit. The Betula nana values reflect this difference in that the highest percentages are recorded at J 12 and Pal 10. Similarly high values are only recorded for the Kil 11 mire site, which in terms of altitude is higher than the R 1 summit (Table 1). It would appear, therefore, that the percentage of B. nana pollen does increase towards the birch woodland/alpine ecotone reflecting the increasing importance of dwarf birch in the vegetation.

(4) The hill summit sites show a much greater range of species than the mire sites (see Table 2), and Lycopodium species in particular are almost restricted to the hill summits. The low Lycopodium values at R 1 suggest that this site, being so close to the forest limit, acts more like a forested site than a treeless one. J 12 stands out as having the most diverse herbaceous flora including some characteristically alpine/arctic pollen types e.g. Dryas, Oxyria, Loiseleuria type etc.




These features are also illustrated by the maps in Figs. 4 and 5. Although this form of presentation allows for only a limited number of factors to be shown, it does demonstrate clearly the spatial relationship between the sites. Thus the relative and absolute decrease in tree pollen as one moves from the pine forest into birch forest (Fig. 4) and the concurrent decrease in pine and increase in birch (Fig. 5) stand out clearly, as do the very low values for spruce at nearly all the sites.

The similarity between the R 1 and K 2 sites, which is especially noticeable in the case of the AP composition, is in keeping with the suggestion that the catchment area is fairly large so that a vegetation region will have a distinct assemblage and variations within the region due to local changes in communities will be subsidiary. There is less similarity between J 12 and Kil 11, although they too are geographically close to one another. The significant factor here is the altitudinal difference which puts J 12 into the alpine zone while Kil 11 is situated within birch woodland.

Comparison with results from elsewhere The features outlined above are those which are evident purely on the basis of the present

moss sample counts. A comparison with other studies will show to what extent these features are distinctive or characteristic. Investigations of modem pollen rain in various parts of Finland, other than those already referred to, have been undertaken by Sorsa (1964), Vuorela (1973) and Kapyla and Koivikko (1975). These have all dealt with rather small areas and often with different aims in mind, but they do allow for comparison on individual points. Similarly the work of Berglund (1973) in S. Sweden, although dealing with more temperate vegetation types does include a mixed boreal forest belt comparable with some of the northern Finnish sites.

Other studies with which a comparison should be made are those from N. America which consider the vegetation belts on a continental scale (especially Lichti-Federovich and Ritchie, 1968; Ritchie, 1974), but unfortunately these do not provide a truely analagous situation since in N. America the forest limit is formed by spruce, there is no birch zone, and the northemomost pines are several hundreds of kilometres south of the tundra. Studies from Greenland (Fredskild, 1973) and Iceland (Rymer, 1973) deal only with arctic/alpine communities so that there is no possibility of comparative values along the transect alpine/ tundra-birch woodland-boreal forest, and studies in Great Britain tend to have concentrated similarly on one vegetation type, e.g. alpine communities (Birks, 1973), pine forest (O'Sullivan, 1973) or, like most of the Scandinavian studies, deal with vegetation types from more temperate areas than those considered here (e.g. Peck, 1973; Tinsley and Smith, 1974; Tauber, 1965; Andersen, 1970, 1973). Nevertheless, the following points are worthy of comment:

(1) The rise in birch pollen and fall in pine as the pine forest boundary is crossed (cf. mire sites point 1), finds a similar situation, but on a much smaller scale, in O'Sullivan's results from Abemethy forest (O'Sullivan, 1973). The same change in the dominant pollen type is seen between his pine forest (S,) and birch woodlands (Ss). O'Sullivan's Betula percentages are much lower than those from N. Finland but then he is dealing with small patches of birch woodland rather than a birch zone.

Unfortunately Sorsa's trap results (1964) from N. Finland, although from sites transecting pine forest, sub-alpine birch woodland and alpine summit, are not really comparable here since they represent only two weeks of the summer during which time birch was in flower but pine not.



726 SHEILA HICKS

SURFACE MOSS SAMPLES collected June 1974

TOTAL POLLEN Ke8

J 12 P9. Kil 11 S N7

a \...... .. ..............

Pal 10

Herbs R 1 Shrubs Trees K2

90,000

60,000

30,000

o.so > 1

.... ..................... 0 50 100 km Northern boundary of pine forest

Fig. 4. Relative and pollen concentration values of total trees, shrubs and non-arboreal species.




SURFACE MOSS SAMPLES collected June 1974

ARBOREAL POLLEN

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Fig. 5. Relative and pollen concentration values for the four main indigenous tree species.



728 SHEILA HICKS

(2) The underrepresentation of spruce pollen relative to the amount of spruce in the vegetation (cf. mire sites point 2) is recorded both in S. Finland and in S. Sweden and is also a common feature of the N. American results. Vuorela (1973) records an average of c. 25% AP for Picea within an area where spruce forest is the regional forest type. Percentages at individual sites vary, but for two forest sites where more than 90% of the trees are spruce, spruce pollen is c. 40% and 30O AP respectively. That the values are noticeably higher than those for N. Finland is probably due to the fact that in the south of the country mature spruce forest is much denser and the trees considerably taller and generally bigger than in the north.

Kapyla and Koivikko (1975) have spruce values of c. 4% AP for both Muhos (approximately the same latitude as H 14) and Turku (S.W. Finland). No information is given as to the composition of the surrounding vegetation since the main aim of the study was to in- vestigate atmospheric pollen in connection with allergy. The values are, however, in keeping with spruce pollen values from areas where spruce plays only a minor role in the forest composition.

Berglund (1973) has values of 11.0% and 8.9% AP from coniferous forest in Sweden in which spruce is one of the dominant trees. These values are compatible with those from mixed pine-spruce forest in N. Finland (A 5 -11.0% AP, H 14 -6.5% AP). Also comparable with the N. Finnish situation is the drop in spruce pollen percentages to values of less than 5% AP as soon as one passes into areas where spruce is absent or only occasionally present.

In the N. American results, however, percentage values for spruce are generally higher than in N. Finland, even though there too it is still obviously underrepresented. For example, in spruce-dominated forests close to the tundra in N. American spruce forms c. 25-35% AP in sediment samples and up to 30% AP in moss samples (Ritchie, 1974), as opposed to 12-22% AP in the present moss samples from Lapland. The higher values may be partly due to the low presence of tree species other than spruce in these northernmost forests (only larch, birch and alder are mentioned by Ritchie as being occasionally present). In this case, although the pollen production of spruce is low, the percentage that it forms of the total arboreal pollen will be high, higher than in the Finnish situation where quantities of birch and pine are always sufficiently close to contribute a large amount of pollen to the AP sum and de- press the spruce percentage.

Another explanation could be the difference in pollen production between the European and the N. American species. Indeed, throughout the different vegetation zones of N. America spruce pollen percentages are consistently higher than in Scandinavia. For example, for the mixed spruce-pine forests Lichti-Federovich and Ritchie (1968) have spruce pollen values of up to 45% XP and for tundra areas beyond the limit of spruce forest, spruce pollen can form up to 20% EP. Other factors are obviously involved in that the big pollen pro- ducers pine and birch which are characteristic of the Scandinavian forests occur in relatively low percentages in N. America, max 33% and 15% of the total vegetation respectively, and Populus, whose pollen frequently goes unrecorded, can form up to 20% of the forest in N. America while it occurs much more sporadically in Scandinavia. Both these factors would result in higher spruce pollen percentages. Similarly, in the case of the tundra, spruce values may be higher simply because spruce is the tree which is found growing nearest to the tundra, which role in Finland is played by birch and pine. Obviously a comparison in terms of absolute pollen frequency is necessary to elucidate the true reason(s) behind the differences.

The extreme localness of a high proportion of the NAP and the consequent high degree of variation in its composition from site to site (cf. mire sites point 4) has long been known




from peat profile studies and is indeed a common feature of modem pollen rain investigations where the samples are from moss polsters (Bartley, 1967; Fredskild, 1967; O'Sullivan, 1973; Vuorela, 1973; Ritchie, 1974; Tinsley and Smith, 1974). Nevertheless, the increasing total NAP percentages as one moves northwards from the closed boreal forest, which appears as a distinctive feature in Aario's results and also comes out clearly in the present work e.g. N 7 -5.5%, -P 9 -15.0%, -Ke 8 -20.0%, -Kil 11 -27.0%, does not find an analogy in N. America e.g. averages of 5.5% for closed coniferous forest, -7.5% for open coniferous forest, -17.0% for forest tundra (Lichti-Federovich and Ritchie, 1968) even though the exact vegetation communities involved are different. The very low NAP values in closed coniferous forest are characteristic and serve to distinguish this type of forest from more southerly ones where deciduous trees are also present.

(4) Pollen analysts are well aware of the high pine pollen percentages resulting from long distance transport in connection with Late-glacial time in N.W. Europe, and Aario's results from Finland clearly demonstrate the dominance of pine among the AP spectra in the tundra. The present high values for long-distance pine recorded on the hill summits (cf. hill summits point I) are therefore not remarkable, but the actual percentage values involved are of interest. The following values have been recorded for tundra or alpine regions well beyond the limit of pine forest:

Site Distance to pine forest % XP

Fredskild (1967) W. Greenland >1000 km 2 grains out of 15,333 Fredskild (1 973) S. Greenland >1000 km 1% Ritchie (1974) Mackenzie delta >1000 km av. 2% Rymer (1973) Iceland >1000 km 2% Bartley (1967) Ungava 800-900 km av. 4% Birks (1973) W. Scotland some small areas on none recorded

mainland to east but winds predominantly from west

Lichti-Federovich Keewatin 200-500 km av. 22% and Ritchie ( 1968)

These may be compared with the present results from Finland of av. 34% XP at a distance of only 50-100 km from pine forest.

From this it would appear that there is a critical distance of somewhere between 500 and 800 km from extensive pine forest beyond which pine is represented in the pollen spectrum at values of less than 5% ZP. On the other hand, in these areas far from pine forest, the percentage presence of pine in the AP spectrum is highly variable, sometimes reaching almost 1 00o AP. This is because all the arboreal pollen, not just the pine, is travelling similarly long distances. This is true for all cases except the Mackenzie delta where pine forms only 3% AP but in this area extraregional pollen is of relatively low occurrence and the forest-tundra zone is fairly narrow so that spruce and alder may be only 50 km distant from the tundra site (Ritchie, 1974).

As one approaches closer than 500 km to extensive pine forest the amount of pine pollen in the total pollen spectrum rises significantly although the percentage that it forms of the total AP may fall. The Finnish values represent a situation very close to the pine forest limit. Obviously the direction of the prevailing wind relative to the position of the nearest pine



730 SHEILA HICKS

forest will be an additional factor, and the exact percentage values will depend on such other factors as the pollen-producing potential of the local vegetation of the sampling site and the neamess of the site to woodland or forest composed of trees other than pine. However, the limit of Pinus pollen at less than 5% EP for a distance from pine forest of more than c. 800 km does seem significant. At the other end of the scale Pinus values of more than 70%o P represent sites within pine-dominated forest and between these two extremes one finds a continuum representing both sites at a considerable distance from pine forest and sites situated within mixed forests in which pine is one component. A more precise delimitation requires both a larger number of results and absolute pollen frequency values.

(5) The increase in dwarf birch as one moves from open forest to the treeless vegetation of higher latitudes and altitudes (cf. hill summits point 3) is clearly seen in N. America (Ritchie, 1974). Similarly, results from arctic/alpine investigations where the pollen of dwarf birch has been distinguished from that of tree birch show high dwarf birch percentages (Fredskild, 1967, 1973; Rymer, 1973).

(6) The greater range of species within the hill summit sites and the characteristic presence of Lycopodium spores there (cf. hill summits point 4) are in keeping with the results of modern pollen rain studies in arctic/alpine areas (Bartley, 1967; Fredskild, 1967, 1973; Birks, 1973; Rymer, 1973; Ritchie, 1974). However, the high values for Gramineae and Cyperaceae which are a constant feature of these studies are not a significant feature of the Finnish results, possibly because the hill summits are not strictly comparable with tundra in respect of the mosaic of vegetation communities represented.

POSSIBLE APPLICATIONS

Since the main aim of this type of modem pollen rain study is to help in interpreting fossil pollen assemblages it is necessary to find some simple means of characterizing and classifying the modem assemblages so that their comparison with the fossil ones will be meaningful. The very small number of samples considered here does not allow for any sophisticated statistical treatment and so a visual graphical presentation has been sought. The modified triangular graph presented in Fig. 6 affords a simple method for classifying results from boreal forest. Only the three main tree species are considered and for each site a point is plotted which represents the percentage presence of these three (i.e. Pinus + Betula + Picea = 100%). In practice two positions are given for each site, one including and the other ex- cluding Betula nana in the Betula sum, but in reality the inclusion of dwarf birch pollen causes only a very slight shift in the position of the sites.

On the basis of the relationship between the present regional vegetation and the pollen results, the graph can be divided into four basic areas:

(i) Sites with Betula pollen more than 60o, which are characteristic of birch-dominated woodland (Ke 8, Kil 11).

(ii) Sites with Pinus values more than 70o which are characteristic of virtually pure pine forest (N 7).

(iii) Sites with Picea pollen more than 12%, Betula pollen less than 60o and Pinus pollen less than 70% which are characteristic of spruce-dominated forest (K 2, R 1).

(iv) Sites in which Betula pollen is between 18 and 60%, Pinus Pollen between 28 and 70o and Picea pollen less than 12%. This section represents primarily mixed forest (A 5,




H 14, P 9) but also includes the hill summit sites in which long distance transport pollen is important (Pal 10, J 12).

Although this graph separates the main boreal forest types it fails completely to distinguish the 'tundra' assemblages. Naturally a system based entirely on AP will always fail to do this since, as is clear from the points outlined in the previous section, the distinctive features of the arctic/alpine sites lie in the NAP composition, and the AP, which is entirely extraregional, will vary wildly and in most cases consists of a very few grains. Bearing this in mind, any unknown assemblage which, if plotted on the graph, is located in the 'mixed forest' section should be inspected further with reference to its NAP/AP ratio and species composition before being designated as characteristic of mixed boreal forest.

Pinus

0 \10 20 30 40 50 60 70 80 90 100./.

/Pi~~~~~~~~~~~~~~~

100 90 80 70 50 40 0 20 10 0'.

Betul a

Birch dominated Spruce dominated LIIJ Pine dominated

A inc. Betula nana A ex. Betula nana

* Kuusamo pollen trap results 1969/ 70 ( inc. Betula nana)

Fig. 6. Modified triangular graph delimiting the main forest types on the basis of their arboreal pollen composition.

It should also be noticed that the R 1 site, which rises only a small distance above the surrounding forest, reacts more as a forest site than as an open hill top since the bulk of its pollen comes from forested areas.

As Fig. 6 is constructed on the basis of a very small number of samples it is natural to question whether it is really significant at all. In order to test this the counts from seven- teen pollen traps, all located within the general spruce forest region of Kuusamo (Hicks, 1974), were treated in the same way and plotted on the graph. As can be seen, all but three fall within the area of the graph that has been designated as representing spruce dominated forest, and of these three, two fall very close to the boundary (i.e. 10 and 11% Picea respectively) and the third, which falls within the pine dominated section of the graph, is indeed from within a locally pine-dominated area. The Kuusamo trap results, therefore, support the above division of the graph with the limit for spruce dominated forests being in the region of Picea pollen 12% of the Pinus-Betula-Picea sum.

CONCLUSIONS

The moss sample analyses considered here, although coming from a relatively small number



732 SHEILA HICKS

of sites, do present differing pollen spectra, and a comparison between these and the results from other areas shows that these spectra can be considered characteristic for the vegetation zones they represent. Since detailed work in N. America (Janssen, 1973) has shown that the main features of each pollen spectrum reflect the regional vegetation type and vegetation differences at the level of the local community produce relatively minor variations, the paucity of sampling sites within each vegetation type in this study is not a disadvantage.

The vegetation types sampled here have the following distinctive pollen features:

Open treeless hill summits NAP important and containing a wide range of taxa including Lycopodium. and typical

arctic/alpine species. Betula nana significantly present. AP composed of long distance transported pollen with pine predominating.

Birch woodland Betula more than 60% of the pine-birch-spruce sum. NAP 20-30% EP. Low pollen

concentration.

Pine dominated forest Pinus more than 70% of the pine-birch-spruce sum. NAP less than 10% EP. High pollen

concentration.

Spruce dominated forest Picea more than 12% of the pine-birch-spruce sum but Pinus and Betula both present in

quantity. Low arboreal pollen concentration.

Mixed coniferous forest Pinus, Betula and Picea all present but Pinus less than 70%, Betula less than 60% and

Picea less than 12% of the pine-birch-spruce sum. Total pollen concentration high but arboreal pollen concentration lower than in pine-dominated forests.

In all cases if pollen concentration, or preferably absolute pollen frequency values, are available, the delimitation of the different vegetation regions can be made more precisely. Results from the pollen traps will add this extra dimension and should help to elucidate the differences between vegetation types which are largely a matter of the differential pollen production of the species involved. Two vegetation types for which such information obviously forms a distinguishing feature are spruce dominated forests and arctic/alpine communities. Preliminary results from Kuusamo (Hicks, 1974) have already indicated fairly low AP frequencies for spruce forest there, and Fredskild's work in Greenland (Fredskild, 1973) demonstrates that in tundra vegetation the absolute pollen frequency is significantly low.

Absolute pollen frequency values will similarly prove invaluable in distinguishing between long distance transported and locally produced pollen when comparing samples which otherwise have similar relative AP values.

The moss sample analyses demonst-r-at-e that the main regional features are distinguish- able and so the choice of sites for the pollen traps seems justified. One additional advantage in working in northern Scandinavia is that a range of different vegetation types is available in a relatively undisturbed condition which can be compared and contrasted one with another, and which at the same time form a continuum. Since the ultimate aim is to use the modern pollen rain results to interpret fossil pollen assemblages from N.W. Europe, northern




Fennoscandia may prove to be a key area in that it is one of the few places where a sequence of vegetation types in any way comparable with those which must have occurred in Europe during the early part of the Flandrian can still be found.

ACKNOWLEDGMENTS

I am most grateful to Professor J. J. Donner for many discussions on the problems of modem pollen rain studies and for critically reading through the manuscript of this work. Pro- fessor K. Kuusela provided information with respect to the forest inventory material, Fil. Lic. Tauno UJlvinen and Mr Martti Ohenoja kindly identified the moss and liverwort species for me, Mr Peter Russell gave useful advice in connection with the triangular graph and Mr Malcolm Hicks provided invaluable assistance with the field work. To all these people I express my thanks.

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modern pollen rain in finnish lapland investigated by analysis of surface moss samples

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